The invention relates to a luminaire and in particular, a luminaire for distributing light from a light source, such as a high powered lamp.
One of the problems with interior lighting of large buildings such as warehouses, factories or exhibition halls, is ensuring that light from the light source is distributed sufficiently evenly over the floor area. In addition, it is important to ensure that the glare from the light fitting is minimised. A typical figure for glare from a fitting is that the glare should be below 10,000 cd/m2 for viewing angles below 50xc2x0 elevation.
In accordance with the invention there is provided a luminaire for distributing the output of a light source, the luminaire comprising:
(a) a mount for said light source,
(b) a central reflector positioned so as to reflect the output of the light source, the reflector being convex towards the light source, and
(c) a light transmitting and spreading device surrounding the central reflector and positioned so as to receive the light reflected by the central reflector, wherein the light transmitting and spreading device comprises an optical sheet material having a structured surface for deviating and spreading the light transmitted by the sheet.
The term xe2x80x9clightxe2x80x9d, as used herein, refers to electromagnetic radiation in the ultra violet, visible or infra-red regions of the electromagnetic spectrum.
In one embodiment of the invention the central reflector is surrounded by one or more additional reflectors, the outermost of which is concave towards the light source. An advantage of such an arrangement is that by providing two or more reflectors angled relative to each other it is possible to provide a luminaire which spreads light to below the luminaire and also to the sides of the luminaire. Preferably, the central reflector has a central axis which is coincident with the central axis of the additional reflector(s). In one arrangement, the central reflector comprises a conical shape tapering towards the light source, and a second reflector surrounding the central reflector comprises a hollow frusto-conical shape tapering away from the light source.
In an alternative example of the invention, the central reflector comprises a number of triangular planar reflecting surfaces which define a pyramidal shape pointing towards the light source. Typically the pyramid defined by the surfaces of the central reflector may be eight-sided. A second reflector, surrounding the central reflector, may take the form of a hollow truncated pyramid with the same number of sides as the central reflector, but tapering away from the light source. Such a reflector comprises surfaces in the shape of quadrilaterals, each having one pair of opposite sides parallel and one pair of opposite sides convergent, the quadrilaterals being mutually linked by their convergent sides. Preferably, the second reflector is mounted adjacent to the peripheral edge of the central reflector which is remote from the light source.
The reflector(s) may be formed from any suitable reflective material, preferably a specularly reflective material, such as metal, metallised glass or metallised plastic film, or mirror film as described in U.S. Pat. No. 5,882,774 and WO 97/01774.
A spreading device is positioned so as to collect and spread the light reflected by the reflector(s). Preferably, the spreading device comprises at least a first spreader formed from the optical sheet material in the shape of a hollow truncated cone or pyramid whose central axis coincides with the central axis of the central reflector, and which is concave towards the reflector(s). When there are two reflectors, the spreading device preferably additionally comprises a second spreader, which is also formed from an optical sheet material, the first and second spreaders being positioned so that the first spreader collects and spreads light reflected by the central reflector, and the second spreader collects and spreads light reflected by the second reflector.
The second spreader is preferably mounted adjacent to the peripheral edge of the first spreader which is remote from the reflectors.
The second spreader typically (but not necessarily) is in the shape of an annulus or annular polygon.
Typically, the second spreader comprises a number of quadrilateral spreader surfaces having one pair of opposite sides parallel, the quadrilaterals being coupled to each other at the non-parallel sides to form an annular polygon. Typically, the first spreader also comprises a number of corresponding quadrilateral sections which are coupled to each other at the non-parallel sides and form an annular polygon around the external periphery of the second spreader.
The luminaire also includes a lamp mounting mechanism to permit a light source to be mounted in the luminaire. Preferably, the light source may be mounted in the luminaire via a central aperture in the spreading device. Typically, the central axis of the aperture is substantially coincident with the central axis of the central reflector. In the case in which the light source emits light in a cone and the mount is arranged such that the axis of the cone is coaxial with the centre of the central reflector.
In normal circumstances, the axis of the emission cone is vertical, with the light being emitted upwards towards the central reflector, which diverts it sideways and downwards through the spreading device to illuminate a large floor area. While acceptable results can be obtained using a single reflector and a single spreader, this arrangement may leave a small area immediately below the light source under-illuminated. Use of a second reflector, angled relative to the central reflector as described above, ensures that a proportion of the light is reflected substantially vertically downwards, so that it may be collected by a second spreader and distributed over the area immediately below the lamp.
The spreading device may be a transmission device which spreads the incident light. Translucent glass or plastic diffusers may be employed but preferably the spreaders comprise an optical sheet (e.g. a film) having a structured surface to deviate the light. Such optical sheets are known and disclosed, for example, in U.S. Pat. Nos. 4,657,355, 5,551,042 and WO91/18304. Suitable optical sheets may have a structured surface comprising an array of Fresnel lenses, particularly an array of negative Fresnel lenses, or two crossed cylindrical Freenel is lenses. Other suitable optical sheets are described in our co-pending PCT Patent application Ser. No. 09/646,362 filed on the same day as the present application.
As a further alternative, two transparent sheets having a linear structured surface may be used, the sheets overlapping each other with the directions of the linear structures at substantially right angles to each other.
In one example of the invention, the luminaire may comprise a third reflector which may reflect optical radiation from the central reflector to the spreading device.
The use of generally conical reflectors in luminaires in which light is emitted vertically by the light source is known, as may be seen from U.S. Pat. Nos. 5,184,550, 5,105,347 and 4,536,828.